Microsoft is pulling out all the stops to promote its new Surface tablet as a worthy alternative to the iPad. The company is rumoured to have spent $US400 million ($384 million) on its marketing campaign.

But there's one stop it probably wishes it hadn't pulled out: getting Oprah Winfrey to tout the device on her Twitter account.

"Gotta say love that SURFACE! Have bought 12 already for Christmas gifts," she tweeted to 14.9 million Twitter followers.

If Oprah can do for a tablet anything like what she can do for a book, Microsoft should see some big sales. There's just one problem. Oprah - or whoever was tweeting on her behalf - was tweeting from an iPad.

There are three plausible ways this could have happened, and none reflects particularly flatteringly on the parties involved. One is that Oprah gets paid to promote the Surface but actually prefers the iPad. Another is that it isn't Oprah tweeting from Oprah's account, and her secret surrogate prefers the iPad.

The third is that Oprah does in fact love the Surface, but is forced to tweet from her iPad because the Surface lacks an official Twitter client. But even that is embarrassing for Microsoft, as TechCrunch points out, because it highlights the fact that major app developers such as Twitter have not exactly been making the Surface a top priority.